Robin Jade Conde

PODCAST: Indoor air quality and mold in commercial buildings (with Neil Carlson)

In this conversation, Reuben Saltzman and Tessa Murry interview Neil Carlson, a public health specialist with expertise in indoor air quality and mold. They discuss various mold-related topics, including its causes, identification, and remediation. Neil shares insights into his work in commercial and residential buildings, highlighting common problem areas such as air handling units, basements, bathrooms, and attics. He also emphasizes the importance of understanding the building as a system and considering factors like humidity control, filtration, and ventilation. The conversation concludes with a discussion on the impact of cooking on indoor air quality. The conversation covers various topics related to indoor air quality, including the effects of particulate matter on health, monitoring for particulates in buildings, the importance of range hoods in kitchens, unique cases of mold growth, dealing with mold in homes, cleaning ductwork, and the challenges of sub-slab ductwork. Neil Carlson provides insights and recommendations based on his building science and HVAC systems expertise.


Mold growth is a common issue in commercial and residential buildings, with problem areas including air handling units, basements, bathrooms, and attics.
Understanding the building as a system is crucial for addressing mold and indoor air quality issues, considering factors like humidity control, filtration, and ventilation.
Proper maintenance and cleaning of HVAC systems, including air handling units and coils, can help prevent mold growth.
Designing buildings with appropriate materials and insulation can reduce the risk of mold growth.
Cooking can contribute to poor indoor air quality, with high particles generated during cooking. Particulate matter, tiny particulates, has a strong negative impact on people’s health, and it is often created indoors from cooking and other sources.
Monitoring particulates in buildings, especially kitchen areas, is important for maintaining good indoor air quality.
Range hoods are crucial in kitchens to remove pollutants and particulates generated during cooking.
Unique cases of mold growth, such as mold growing inside countertops and bagpipes, highlight the importance of proper maintenance and cleaning.
Dealing with mold in homes requires caution, especially for individuals with compromised immune systems, and professional help may be necessary for larger mold problems.
Cleaning ductwork can be beneficial if done correctly and thoroughly, but it can also create problems if not done properly.
Sub-slab ductwork that continuously gets wet is difficult to address, and the best solution may be to fill it in with concrete and go with an elevated system.
Using portable HEPA filtration systems can help improve indoor air quality, but it’s important to oversize the filter and adjust the airflow to minimize noise.
Understanding geology and drainage is crucial when dealing with sub-slab ductwork to prevent moisture and mold issues.


00:00 Introduction and Guest Introduction
01:36 Neil Carlson’s Background and Expertise
06:15 Common Problem Areas in Buildings
11:21 Identifying Mold in Homes
15:28 Mold Issues in Commercial Buildings
21:23 The Impact of Cooking on Indoor Air Quality
29:02 The Impact of Particulate Matter on Health
30:20 Monitoring for Particulates in Buildings
32:38 The Importance of Range Hoods in Kitchens
33:07 Dealing with Mold in Homes
37:54 Cleaning Ductwork: Benefits and Challenges
41:46 Challenges of Sub-slab Ductwork
45:17 Understanding Geology and Drainage in Sub-slab Ductwork
50:50 Using Portable HEPA Filtration Systems



The following is a transcription from an audio recording. Although the transcription is largely accurate, in some cases it may be slightly incomplete or contain minor inaccuracies due to inaudible passages or transcription errors.


Reuben Saltzman: Welcome to my house. Welcome to the Structure Talk Podcast, a production of Structure Tech Home Inspections. My name is Reuben Saltzman. I’m your host, alongside building science geek, Tessa Murry. We help home inspectors up their game through education, and we help homeowners to be better stewards of their houses. We’ve been keeping it real on this podcast since 2019, and we are also the number one home inspection podcast in the world, according to my mom. Welcome back to the Structure Talk Mold Month, no, Mold Year. This is the year of mold discussions for us. Tessa, great to see you. How are you doing today?


Tessa Murry: Hey, Reuben. I’m doing well. How are you?


RS: I’m fantastic. Thank you. We’ve been on quite the kick lately. We’ve been talking a lot about mold and indoor air quality, and we are not done. We’ve got more on it. We just, there’s so many people that we know and there’s so much to talk about. There’s so much interest around this. Well, Tessa, why don’t you introduce today’s esteemed guest to us?


TM: So I’m so excited and honored to welcome Neil Carlson to the show today. Neil, I’m going to try and introduce you to the best of my ability, but I apologize in advance. I met Neil through the University of Minnesota when I was teaching this past semester with Pat Hellman. He was a guest lecturer for one of our classes on indoor air quality. And I think Neil is probably, I don’t know, you’re definitely top three people I’ve ever heard or met that understands indoor air quality issues and mold. You, I mean, you can look at a sample of mold under a microscope and know exactly what type of mold it is, the conditions it causes, where it grows, why it grows, all of that and what to do about it. But you also understand the building science and, you know, what to look for and how to identify problems and what to do to fix it. So I am so excited for you to be here on the show today. You’ve got, what is your background, Neil? I know you’ve got, what is it, a Master’s, I think, in Environmental Health from the University of Minnesota. Is that right?


Neil Carlson: Yeah, I was a Master of Environmental Health. They actually, after I was in there for a year, they said, we can switch it over to Industrial Hygiene. And I said, that sounds good. And they said, it’s free tuition. I said, that sounds better.




NC: Why not?




NC: Yeah. And as a plug to it, we do have that program is still going on because we’re short of industrial hygienists. And so NIOSH funds it. And I’ve been, myself and some other grad students have been recruiting people for the program. But it’s a really interesting piece of work. Every day is completely different from the previous one.


TM: Wow. I want to dive into that with you. And you also, don’t you have a background, don’t you have a bachelor’s in like chemistry and biology too?


NC: Yeah. Mass or a major in biology and then a minor in chemistry. And then I came close to a psychology degree, which has become more helpful as life’s going on.


TM: Of course. Well, well-versed, well-versed. So I guess I’d love to hear, Neil, a little bit about what is your title? What do you do day to day? And how did you get there? Let’s hear about your journey.


NC: Yeah, public health specialist. I started out as a technician and shifted over after a year. I got into the usual way where my application was rejected initially, and then I worked through the system, got them to extract it from the HR system so I could get interviewed. And I thought it was… That’s the way they’d fixed it, but we had a similar problem with somebody like 20 plus years later. So I think there’s some consistency in the hiring practices, which is always comforting. The typical day or typically what we get involved with are, it varies, but we have the emergency response side of it where we have things blow up and we have to try to fix things afterwards. Like when we had the sewer explosions, the manhole covers are flying all over and then we try to figure out, okay, why are they flying all over and why is my VOC meter like this and sometimes like this? And then the lower explosive limit is like this and the VOC is down like that and they aren’t tracking together.


NC: So that was interesting. Then the other part is we do frequent indoor complaints. Either somebody will complain about they’re in a building and they aren’t feeling well. Or we start off, let’s just check the filtration. So we’re checking the filtration efficiency and it’s lousy. And then we’re looking at the air handling and it’s completely overgrown with mold. They said, well, it’s just because there’s a leak. Well, let’s look at the next air handling unit. That one’s bad. The next one’s bad. Well, maybe the whole side of this campus is bad. So then we start looking some more and more. Then we find out that somebody who was supposed to be maintaining it was kind of not doing anything.


RS: Oh gosh.


NC: And the coil is completely occluded with dust. Then you, okay, so then we say, well, let’s put some filters. And then we find one guy who’s kind of a savant and said, I figured out that if we put MERV 13s in here without a pre-filter, I think it’s going to be okay. His was pristine. Everyone else is a complete mess.


TM: Wow. So you kind of, you’re a problem solver. You come in when there’s a complaint typically, and it’s a lot of times sparked by health issues, health concerns with people?


NC: Right. Usually we get called in when they’ve been trying to solve the problem, they haven’t solved the problem. So then they’ll bring us in. Either one is be through an accommodation like a person has a specific problem related to disability services or workers comp claim. We try to figure out what’s going on there. Or it’ll be a generalized thing. We’ve got a problem in this whole area, what’s going on? Or like in a couple of cases where there’ll be a sentinel event like there’s some mold growing in a dorm room and then we’ll look and there’s a recirculating fan coil unit that’s problematic and then we have to ask the question, well, could there be more that are similar and if there are more that are similar then we have to address it that way.


TM: And then you try and figure out how to fix it, right? If you’ve got mold growing inside of this A-Coil or this air handler or what have you, duct work, then you have to figure out, okay well, why did it happen in the first place and what do we do to prevent it from coming back, right?


NC: Right, and it’s somewhat problematic preventing it. I mean, you’re looking at an existing air handling unit with a fan that’s designed for a specific static pressure drop. And if you switch from a MERV 8 to a MERV 13 and the fan can’t handle it, then you’re in the wrong part of the fan static pressure, and your fan can’t blow any air, so then you have to make an accommodation, what’s a reasonable amount of filtration that you can do to reduce the dust loading that’s one of the initial causes of mold growth? But then there’s the design where, for some strange reason, they decided to put paperback… Chill water inside the unit where we’re blowing water right off the coil, and so why is there mold growth? Well, you provided mold chow and you provided dust with lousy filtration and then you have a completely overgrown air handling unit.


RS: So just about everything you’re working with is going to be on the commercial side, is that right?


NC: No, no. I get pulled in on housing, which has been interesting because you’ll have really beautiful homes, like six or seven air handling units, and it’s a complete mess and nightmare. The place I was involved had its own theater.


RS: Wow. That’s a big house.


NC: Yeah, and they all had moldy ducts. And so we were running HEPA filters and the air is super clean. I’m looking at the aerosol samples and this is really clean and all of a sudden it just loaded up with penicillium spores. So even though they’ve been running the HEPA filter for a long time, they still had enough background penicillium that was being stirred up by the HEPA filters that was causing problems.


RS: Wow.


TM: Oh my gosh. You know, there is such a need for people like you, Neil, you know, and just even I think there’s been, you know, increased awareness around indoor air quality, especially since COVID, you know, and trying to maintain healthy indoor air environments. But there’s just so many cases of people getting sick, feeling unwell, mold growth. And, you know, it’s just such a pervasive problem. Do you primarily deal with, would you say like 90% of the cases you deal with are mold related? Or do you deal with other stuff like VOCs and radon and all of that?


NC: It’s a little bit of a mix. I’d say primarily mold because I think in part because of our climate, I mean, there’s problems. I was working with a university down in Texas and they’ve got high humidity and mold and it’s constant there. But with us, we’re trying to design a building envelope that can really work well in the cold and then really work well in our humid times that we have from July, sometimes from June through August, maybe a little bit into September. So we’re trying to figure out how to get the building envelope right in that context and we’re trying to run the air handling unit and we’re also trying to conserve energy. It’s a tough go and a lot of people will say, well, let’s take out the reheat coils because they’re really expensive. Well, if you take the reheat coils out, you aren’t taking enough humidity out, and you end up with mold growing on the supply diffuser.


RS: I’m sorry, basic question, what’s a reheat coil?


NC: Well, reheat coil would be like if you have a thermostat in a room. There’s a coil in there that modulates the temperature, so the air will come in, let’s say at maybe around 55 or 58 degrees, comes in, it’s a little bit too cold, so you turn the thermostat up, heats up the air, so when it comes into the space, then it’s modulated and it’s at the temperature that you want. The other way that would be manipulated would be a VAV box, would be a variable air volume system.


RS: And this is only on commercial systems, right? I’ve never seen anything like this.


NC: Yeah, that’s typically on commercial systems.


RS: Okay, and that reheat box, is that an electric resistance heater? How does that heat the air?


NC: Well, sometimes it’s a steam reheat. So you have a steam system going in there, it will put it in a coil. And it’s often, if you don’t have proper filtration, it’s often an area where you’ll get particles deposited on that. So when you’re cleaning the ductwork, you have to make sure you clean it in sequence, ’cause if you clean the reheat coil but don’t clean any other part, you turn it back on and all the dust that’s been deposited in that system will go through the clean reheat coil and fill up a lab with approximately a quarter inch of fine dust.


RS: Wow.


NC: And then you have people get fired because they didn’t think it through.


TM: Of course. Well, you know, we’ve talked a lot about mold on this podcast before, and we’ve had on some experts in mold as well, just kind of sharing where they commonly find mold in homes. And I’m sure you’re aware of this too, like kind of some of the top, like five places you might find mold. You know, we’ve got a lot of basements here in Minnesota, and that’s a common place. People want to finish their basement. Next thing you know, they’ve, you know, got moldy carpet, mold growing behind the drywall against the foundation wall. Lots of issues there. Bathrooms, of course, places of high moisture. Even in the attic space, you know, from air leakage and that warm, moist air rising and leaking up into the attic when it’s cold outside and that moisture condensing on the roof deck and causing staining and eventually potentially mold growth too. So we have all these potential places to look in houses. What about, where do you see most of the problems in the buildings that you’re working with? Is there a pattern at all? Like, are there like top five most common places you find issues?


NC: There’s a couple. One actually is external and so we had to deal with that with our arboretum. So they had this massive compost pile. It wasn’t that massive, it was okay. But then the county said, hey, you have a compost pile, can we add on to it? They said, sure. Well, it got bigger and then we had a NIMBY situation, which was not in my backyard. Wind directions from the right spot, lots of Aspergillus fumigatus. And so then they had to move the pile more centrally so if you get about, it’s about 850 feet away from it tends to drop off pretty good and you get background, but if you’re doing sampling for it you’d sample at 25, you’re just going to see outdoor air stuff, you sample at 35 then you’ll pick up the fumagatas, so, and you couldn’t see that if you’re looking at it with an aerosol cassette so you have to do culture samples, so now let’s roll it back into the house. The ice machine, full employment. Underneath the sink, full employment. You know, water all the time. Corners, especially apartment complexes, corners in closets where they’ve designed it. It’s poorly ventilated. The closet door is shut in the wintertime. And it’s also at angle, so they don’t do a nice job on it. It’s also round electrical sockets. Windows, terrible.


RS: And an outside wall, I bet.


NC: Outside wall, yeah. When you see the glacier on the inside, you say, hmm, maybe it needs a little help. Next part, along the exterior wall, carpet tack strip. When I’m doing an inspection for somebody who wants to buy a home, it’s essentially a, usually a former grad student or somebody says, hey, can you take a look? So if I get permission to peel back that, look at the carpet tack strip, look at the rust stains, look at the condition, if the tack strip is essentially powder, then I said, well, if you want to buy this house, your whole building envelope is problematic. So it’s a lot of nice information from a really small area. And then of course, pulling back the carpet, looking at the concentric rings from the past water infiltration. Of course the HVAC system can be problematic. Basements are always, the finished basements are problematic. Looking at houses without adequate gutters.


TM: Yeah. We’ve got so many questions. [laughter] Okay. So you’re primarily dealing though, a lot of the time with buildings on the campus, University of Minnesota campus. Is that correct?


NC: Yes, that’s a practical one. Yep.


TM: Okay. And so I know from some of the case studies you shared in class, you were dealing a lot with air handlers and heat coils and stuff like that in dorms and then also some of the other major buildings on campus, right? That was a common place to see mold growing was in the HVAC system that was circulating the air. Is that correct?


NC: That’s correct, yeah. Yes.


TM: Okay. Okay. And are those ongoing issues or do you think that someone like you can come in, see what’s going on, you have a solution to it, and it can be fixed, and then you just kind of monitor it over time? Or are a lot of these issues that you’re coming across on campus, like, just, they’re complex and complicated, and it’s not an easy solution, and there may not be an affordable solution that makes sense?


NC: They’re both.


TM: They’re both. [chuckle]


NC: So for the dorm rooms, there’s a straightforward compact unit. If you clean, in some cases you have to do this, you clean the fiberglass on the interior lining, which is not generally recommended, but if you have to do it, you have to do it. So you clean that.


RS: Wait a minute. Pause. How do you clean that?


NC: It’s hard. You HEPA vacuum it. You treat it with, let’s say, a… You can treat it with Oxine or another chemical and then encapsulate it with an antimicrobial product. The one we use, I’m not going to be endorsing, I’m just letting you know what we use, which would be Foster 4020. When you’re using that, you have to follow the EPA label and let it dry for a certain period of time before you allow reoccupancy. That product has a 10-year warranty on it. So it works fairly well. They use it in poultry processing or slaughterhouses where they have some problems with it. You paint it on the wall. I’ve only got pulled in on one case where they had one little bit of microbial growth that they couldn’t solve. And it was a particular Ascomycete fungi. It was based off of a type of erosium that was fairly difficult to find, but I was able to tease Tate out of the ASCO store. But generally, really, that’s a positive way. The other part is design it appropriately in the first place so you don’t have exposed fiberglass lining and you have the lining between two pieces of metal. And we try to go that way, but we have a lot of legacy systems around the campus. And so we’re stuck with what we’ve got.


RS: And I just got to ask, I want to make sure I understand this right. You’re saying that you’ve got duct work that has the fiberglass lining on the inside. That’s what you’re referring to.


NC: Yes.


RS: And you’re saying to clean it, use a HEPA vacuum. How the heck do you even get at it?


NC: In the smaller systems, it’s fairly easy. You take the panel off, vacuum it off, and then coat it. The other ones, the larger ones, you put a negative pressure system on a portion of the ductwork so you’re pulling all the dust in there. They’ll either whip it with a whip or they’ll have vacuums that go along it and clean it all the way down to that other section to get as much dust out. Sometimes treat it with some sort of chlorine dioxide based components so you’re fogging it and then you follow up, after it’s dried follow up with an encapsulant, my preference is to remove it but in some cases the cost of that is prohibitive so we make a modification and do it that way. But it’s difficult because we have a lot of, there’s some duct works that are in situations where we have cold condensing surfaces, so the equilibrium relative humidity is higher than what it should be, and then you have mold growth on those. We did have one case where we had, it was asbestos material that had Cladosporium growth over it. So Cladosporium was protecting people from the exposure to asbestos. I’m just kidding. Because it was, it was locked up and we weren’t abrading it, so it wasn’t gonna be put in the air.


RS: Okay. All right. Sorry to interrupt. I just, I…


TM: No, no.


RS: I wanted to make sure I was understanding that right.


NC: Yeah.


TM: And I think I know what kind of fiberglass you’re talking about. It’s like half inch thick, or it’s like a panel kind of, and a lot of times you might see it on the inside of like an air handler unit kind of insulating that box. But then you can also have it in your duct work too. Or it can be the duct work. So then that can be problematic. Okay.


NC: Yeah, it’s usually on the panel. So for instance, if you go into the, a hotel room and it’s a fan coil unit to bring in just maybe a modicum of outside air, recirculating it in the spot. The filter they have is these tiny little fiberglass filters that maybe cut out the dust mites that have invaded the hotel lock those, but it doesn’t do anything with the particles. And I should note, and when we’re talking about particle filtration, the fit is so incredibly important. I’ve been in hospitals where you’ve got HEPA filters and the particle counts are the same stream upstream and downstream from the filters.


TM: Because the air can move around the filter if it’s not fitting properly?


NC: Right. So the wrong filters were delivered and they just put them in anyway.


RS: Sure.


TM: And the air will just bypass it.


NC: Yeah. And so when you’re doing an inspection on it, make sure you got a really nice, tight fit with those. And you put spacer bars or whatever you wanna do, but you can have the best filter in the world, but the air is gonna say it’s really hard working here, but buy gum. It’s really easy to go around here. So let’s just do that. Okay.


TM: So it sounds like you have a lot of like solutions to the problems you see with these commercial buildings and dorms and everything where you can come and you can maybe clean stuff, replace it, control humidity levels, chain shelf filters, treat things. But also you’re saying sometimes it’s just an ongoing battle ’cause of poor design [chuckle] and poor materials.


NC: Yeah. And for instance, we have a spot in one building where they open up the loading dock doors a lot. Well, we have a pipe, even though it’s really well insulated, it’s covered with plastic. So big pipe, cold water covered with plastic, mold growth still grows on the plastic. So they’ve gotta open up the loading dock doors, so then you at least have an easily cleanable surface. The most problematic space on campuses are cold rooms.


TM: Cold rooms, you said?


NC: Cold rooms. They’re walk in cold rooms where you have all these chemicals stored ’cause you have to keep them cold. And then you walk into it and the growth will probably be on the label of the material, any cardboard boxes that are in there.


TM: Wow.


NC: And then if people decide to put a lounge chair in it, that’s probably gonna be pretty moldy too, because it’s surface that can capture all the moisture, and trying to dehumidify those has been problematic. So that’s a source of full employment for myself and my colleague.


TM: My Gosh. I remember you telling about a case study too with I think a library on campus that had started having kind of mold growth happening on all the books, certain books?


RS: Oh no.


TM: Is that right?


NC: Yeah. There’s about 20,000 or 30,000 books. So this is the thought process that you can have when you’re managing an air handling unit. So here’s the initial situation. They had mold growth occasionally on a few books, and then one summer it went really bad. So first problem, outside air dampers weren’t working, so they were open. So we were getting fully humidified air, which would be the way it would be if it’s in a lab building. But we’re in a class B occupancy, so we’re dealing with recirculated air from a library. So we have humid air coming in. Somebody decided to change the temperature of the coil so they would save a little money so it wasn’t taking as much moisture out. The next thing is they weren’t getting the cold temperature that they wanted down in the space below. So they turned up the fan speed. So got all these things working together. I’m walking up there, it’s a fairly humid day in September, and there’s water dripping out, like blip blip blip out of the cooling cold drain pan. So I said, shut the fan off, shut the fan off, and the water pours out. So the fan static pressure is greater than the vertical drop from the drain pan. So we had all those things going on, lost humidity control, and then we had the growth and it was primarily on the cloth covered books, not on any one of the plastic.


RS: Wow.


TM: My gosh. So it’s a mixture of, okay, we need to reduce the amount of humidity coming in, reduce the amount of hot, humid air coming in. We need to slow down the fan speed so that that air moving over the coil will move slower, which will pull more moisture out of the air as it condenses on the cold coils. And kind of all of those things combined would help reduce that humidity issue that they were having.


NC: Right. And because of the occupancy, I mean, we’re not dealing with a lab, so you can bring it down to about 20% to 15% outside air. So you’re recirculating air that’s already been conditioned once, it doesn’t have as much humidity. So you don’t put the system under as much stress.


TM: Wow.


NC: But if you don’t [chuckle], if you only look at one part of the problem, you keep, it’s like a Cohen Brothers movie, you keep making stupid decision after stupid decision, and you end up in a hellish space if you don’t understand the full picture.


RS: Yeah.


TM: I talk about that a lot with, I mean, just with building science in general, just understanding the house as a system and how if you change one thing, you can impact another thing unintentionally. And it’s the same thing with what you do, it sounds like, you’re thinking about all these different potentials and variables and how they’re all impacting this failure that you’re looking at.


NC: Yeah. It’s… Well, it’s interesting because I’ll talk about one part that’s a little unusual. So you’ll get this carpet that’s no VOC, so this is not mold, this is just a VOC. The carpet’s no VOC, the people are complaining about it and they put their chair mat on top of this no VOC carpet, pull back the chair mat on it, VOC levels off the charts. So it’s the definition of VOC. VOC is something that can be photo degraded in sunlight. So it can still have chemicals, but it doesn’t follow the EPA definition for VOC. So a no VOC carpet still has chemicals, but it doesn’t have the chemicals that auto degrade. So just think through that, process that, so when you’re thinking about setting up an office, you just don’t put the chair mat, let it air out, and it should be fine.


TM: Let it off.


RS: Oh, I’m in trouble.


TM: Let these things off gas. Okay. [chuckle]


NC: But…


TM: Oh my gosh.


RS: I put my mat down right away after I put in the carpet, I’m in trouble.




NC: Yeah. Well…


TM: Don’t sniff too deeply. [laughter]


NC: Yeah. I think the other one, this is a little tangential, but this is like a homeowner’s trying to figure out, do I have a mold problem or not, really solve? And so one of the things that I often tell people if they have the lung capacity to do it, they aren’t asthmatic or anything else, just put a N95 respirator on, nice and tight, good fit. They don’t have to fear it or anything. And if they can walk around, they don’t sneeze or anything, great. Take it off. You start sneezing, have copious amount of nasal discharge. Okay. You may have a mold problem. So that’s using your body as a simple, rough idea of whether you’ve got a mold problem or not. And then you can look into it further with a lot of different types of testing or actually visual investigations probably one of the first pieces.


TM: That’s a really helpful tip. And I mean, of course we know not everybody reacts to mold the same way. Some people have severe reactions and some people don’t have any, but if someone is feeling like maybe their house is making them sick, that’s a good test to do. An easy test.


NC: A real simple test. I think the other one that houses aren’t thinking about, just shifting away from mold a little bit, we’re doing some research with Professor Dan Hardin in Architecture. And he’s looking at apartment complexes and homes. And one of the major problems we’re finding out is cooking, huge amount of particles that are generated by cooking. So I brought in a little particle counter just in my house, you know, you got the ventilator and everything else really, high counts, the air fryer’s just horrible. So put a portable HEPA filter right in front of the air fryer, cover it up, essentially making a box fan, box HEPA unit for the air fryer, and then you drop the particle count.


TM: So I just, I wanna touch on this for a second ’cause this was something that was kind of new information to me that I heard for the first time teaching this class this semester with Pat Hellman. That really, it does seem like particulate matter, small particulates specifically are creating some, having a really, really strong negative impact on people’s health in general, more so than we realized. And so, and a lot of times those particulates are not necessarily coming from the outdoor environment. We’re creating them inside from cooking, from all the chemicals, from e-materials in our homes and all that. Correct?


NC: Yeah.


TM: Okay. So are you trying to… Do you monitor for particulates in a lot of these buildings that you work in as well now too?


NC: Not as much because most of the buildings that we’re working in, with the exception of chemistry labs, they aren’t doing a lot of cooking. They aren’t doing a lot of things. I think the areas are probably gonna be more of a focus would be kitchen areas, that type of cooking. And for example, in homes, I think the interesting part is some of the newer HEPA filters actually have built in air quality meters or PM 2.5 meters built right into it. So you get a rough idea of what particle counts you’ve got. So I’m looking at the one in my home, and it’s hitting the same index that we have where it says dangerous to everybody when I’m cooking. So it’s thinking about things like that. Okay. And then the health data saying increased heart attacks, a whole bunch of other things happened just by elevation of fine particulates and then our outdoor air bringing in the tattooing like weather from Canada, you know?




TM: Well, all the smoke, the wildfires. Yeah.


RS: Well, you talk about kitchen issues. And I remember there was a, there was this article, I pulled it up here quickly. It was, I don’t even know how to say this. It’s R-O-C-I-S. It’s all in caps. So I don’t know if you’re supposed to say ROCIS or what it is, but kitchen range hoods issue briefed, and it’s a white paper by Thomas J. Phillips, and it’s a very strong case to have ducted range hoods above every cooking appliance in every dwelling, no matter what. It doesn’t matter if it’s gas or electric, what you’re cooking with, the issue is that you’re cooking, it’s not what type of fuel you’re using for the cooking.


TM: Particulates of cooking.


RS: And Tessa, something I, well, both you guys at the end there’s a list of acknowledgements on who contributed to this, and there’s a name you guys might recognize. Pat Hellman, University of Minnesota.


TM: There we go.


RS: Yeah. Contributed to this.


TM: Shout out to Pat. Yeah.


NC: Yeah, I think the problem with it is the recirculating filter that’s on the unit for the ones that don’t exhaust out, that doesn’t work very well. The second part is…


RS: No.


TM: No.


NC: That we gotta be really careful when we’re designing it. You should slap in a really nice one. You gotta make that air up. Otherwise, we’re back drafting every combustion appliances in that whole place. And then we’ve got dead people, but very clean area in the kitchen.




RS: Yeah. Yeah.


TM: Oh yeah.


NC: So the same thing when you’re thinking about abatement, you’re pulling in negative air, make sure that you aren’t back drafting any of the combustion appliance. We had one spot where we were, we had a huge warehouse where we were storing our books, carbon monoxide coming in, trying to figure out what’s going off, couldn’t figure it out. They’d taken a panel off the air handling unit and it was pulling more air into the space, creating a negative pressure. And we were back drafting the boiler that was in there, pulling the boiler air right into the space and distributing throughout the whole spot. So when you have complex systems with more than one source of combustion, then you can really end up with a problem. Even though we had an outside air pulling air in, it wasn’t sufficient to pull in the outside air.


TM: Wow. And you’ve dealt with some really unique cases too. I remember you talking about some issues with some really unique types of mold growth. And I’m trying to recall, I think one of them, I don’t know if they were related to the U of M, I think one of them was, but can you talk about that mold growth that was growing inside the countertop of one of the egg buildings?


NC: Yeah, it was a poultry necropsy area. So not one of your funnest areas to be where they’re chopping apart birds and trying to figure out if they’ve got, you know, H1N1 flu, we’ve got a brand new facility and all. So this is the old one where they, and they made vinyl countertops, vinyl particle board countertops in an area where you’re spraying it down with water, it’s like a prescription for disaster. So they’re ripping it apart. You’ve got all these feathers and everything else, but the gentlemen that were cutting it apart, breaking it apart, putting it away, none of them had PPE, sent all of them into the emergency room because they were overexposed to stuff.


RS: Oh.


NC: It’s the same thing We had in an agricultural setting, handling moldy Sudan grass, bailed it too early, set it up, guys in there working, another emergency room visit. So when you’re mechanically disturbing something that has a high mold count, then you can have problems. I think the other one that’s more relevant to some of the musical people is of course the death by bagpipe, where the individuals playing a bagpipe goes on holiday to either New Zealand or Australia, comes back, starts playing again, dies. And so they had fusarium rototiller, a specific aspergillus and one other one that was in there. And that caused a problem with sensitized lungs. So if you play a musical instrument and you put water into it, either with a reed or a horn, you need to clean it.


RS: So you’re telling me somebody died from something that was growing in their bagpipe?


NC: Yes.


RS: Wow. Okay. All right. Got it.


NC: So the cool part is we had a student that was complaining about something up at UMD and I told Laura Lot up there, I said, Laura, let’s just sample the instrument that the person’s playing ’cause they were complaining about the general indoor, found three of the four organisms in there. So I said, tell him to clean it out a little better and it should be okay.


RS: Wow.


TM: Oh my gosh. I, you know what, that… I used to play the french horn in middle school [chuckle] and then into high school. And I just think about how gross the inside of that thing would be. And I don’t think anyone ever cleans the inside of their…


RS: You didn’t clean it weekly, Tessa?


TM: How are you supposed to clean that? Wait, Neil, how do you clean a french horn? How do you clean the mold out?


RS: Use french horn cleaner.


NC: Yeah. You hire little french horns cleaners and they go in there and they, they’re just microbots. Yeah.


TM: Seriously? You don’t bleach down it? I mean, what do you do?


NC: I’m not sure. I think, again, I will draw, pull back to follow manufacturer’s recommendations.




NC: But, you know, there’s usually a cloth method that you go down certain tubes, but french horn has got a lot of different spots, so it’s harder to clean it.


TM: And it’s windy and curvy. Yeah.


NC: Oh. Maybe…


RS: Yeah, that’s still getting water and bleach. That’d be my jam.


NC: Yeah. But that way might adversely affect the metals that are on the instrument.


TM: Probably, you weigh the inside of the horn.


RS: Yeah, probably would.


TM: So with this cleanup that you’re talking about, Neil, do you have any recommendations, like for a homeowner, let’s just say they are concerned about mold growth in their house. Maybe they’re, you do this little N95 mask test and they take it off and they realize that they’re having some adverse reactions with their respiratory system, and then they do a visual inspection. And kind of the key areas we’ve talked about, maybe they got a finished basement, they pull up the carpet tack strips and they find mold. Do you have like a protocol or recommendation for how people should deal with mold in their home?


NC: Yeah, I think the thing for people to realize is, number one, what is their sensitivity? If they’re immune compromised, if their lungs don’t work very well, they’re really sensitive to mold, then they shouldn’t be doing the work. Number one, even just wearing the respirator is gonna put adequate excess stress on their cardiovascular system. So if it’s an area that’s a little bit larger than, you know, it’s in the one to 10 square feet, then you probably can have a buddy and you take care of it. If it’s just much bigger than that, then you’re gonna need some help. The other part is, and I was just doing testing at a place where it was a soundproof area where this person had set up a music studio and there was mold growth on different parts of it.


NC: So I took an air sample in a spot and I got about this level, and then I sampled in the same location where I was just doing tease tape samples of it, four times higher just doing tease tape samples. Now, if you’re ripping apart the material, if you’re taking apart, figure the levels are gonna be approximately a hundred times higher than the background level because you’re adding mechanical force onto it. So individuals where you need to wear a respirator, and even if you’re doing the investigation, you should have a respirator on. Because even just simply tease taping areas where there’s suspected mold growth can really increase your risk of exposure. And I’ve had people who haven’t felt very well after doing just the initial investigation.


RS: Interesting.


TM: Wow. Okay. So if you’re gonna disturb a material that you know has mold in it, that’s what you’re saying, just be very cautious with that ’cause it’s gonna release more mold spores into the air.


NC: Anytime you provide mechanical force into an area that has mold then you’re really increasing it. So for instance, a lot of your previous people have just slap a spatula on the carpet. In fact, what I’ll do is take a quiescent or non disturbing sample and slightly agitate the material and the counts are usually fairly high. Vacuuming is another one that’ll… Even with a HEPA vacuum you get about a hundred times higher vacuuming than you will without it. And it stays up in the air, depending on ventilation, probably about an hour and then it’ll drop back down.


TM: Even the HEPA vacuums that are supposed to be sealed release that dust and mold back into the air, you’re saying?


NC: Yeah. We did a research study on coarse and fine Arizona road dust. So you put it on the carpet in specific area and then you change the different types of vacuums up. And even with the HEPA vacuums, it’s about a hundred times, without the HEPA vacuums about a thousand times higher.


RS: Wow.


TM: Oh. Wow.


NC: So if you’re a immune compromised person…


TM: That’s discouraging.


NC: And you’re vacuuming your house, if you can handle a respirator while you’re doing it, that might be a good approach.


TM: And you know what, maybe go as far to say if someone’s having some serious health issues, maybe you should get… Just get rid of the carpet?


NC: Yeah. I mean, that’s been I think…


TM: A good solution.


NC: Mentioned in several places on podcasts.


TM: Yeah. Yeah. What’s your stance on cleaning duct work? Do you think that that’s a good idea or can it create more problems?


NC: If it’s done correctly by people who know what they’re doing, that are very thorough and meticulous, it can be helpful. If they don’t know what they’re doing or they miss one step, it can create a nightmare.


TM: Can you bullet point out for us what they should be doing? Like if you’re a homeowner and you’re looking to hire someone, what should you look for?


NC: Okay. You need to, first off, they need to make, like we talked to before, understand the combustion appliances, make sure that we don’t get any backdrafting with carbon monoxide, dealt with that. Then if they’re cleaning the duct work layout, okay, how are you going to do it? What are you doing first? What are you doing last? Sequence it so that when you’re cleaning, you aren’t cleaning in a spot where you’re half done, you have to turn things back on when you leave and then you cause a big problem with it. The other part is when they’re doing the cleaning, they’re putting the place, the sections that they’re cleaning under negative HEPA filter, they suck all the material out, then they do a final clean on it. And then when they start up the unit, they should bump it like two or three times, turn it on, turn it off, turn it on, turn it off. And then also have a filter over the supply diffuser when they’re doing that.


RS: Hmm. Okay.


TM: Interesting.


NC: That’s a pretty good way to check. And then sometimes I’ve done visual inspections afterwards and they were supposed to encapsulate the fiberglass line duct work, encapsulates white duct works black. Look up there, it’s a Holstein cow. So they weren’t thorough and meticulous, being thorough and meticulous is really a problem. You could have a fire in a house. They’re cleaning up the soot after a fire. First time through, not so good. Second time through, not so good. Third time through, not so good. Fourth time, well, they finally got it. We had a fire in one of our labs and I had to keep coming back and back and back because they didn’t clean up the soot particles.


TM: Wow. What about…


RS: Are there any… Sorry, go ahead, Tessa.


TM: Go ahead.


RS: Well, are there any duct cleaning companies you know of that do residential, that do everything that you just described?


NC: I don’t get involved with them. I deal primarily with commercial. And I will as practical experience, the human beings that are out on the task, irrespective of the company, are the most critical factor. So if you have a really good supervisor, a really good person who’s doing the job, who really understands the full perspective, you’re gonna do well. And you could be from a great company, and if you have.


TM: A new employee?


NC: Well, it goes back to Robbie, the reindeer. Do you remember Robbie, the reindeer hooves of fire?


RS: No.


TM: No. Sorry. [chuckle]


NC: So Robbie the reindeer is being trapped in a prison that was made by other reindeer, by Donner, ’cause they’re all trapped in there, and they’re trying to figure out a way out of the prison. And they said, well, everybody had to build part of this prison. Right. So let’s see where Robbie built it. And Robbie’s is just horrible. So they were able to break out of the prison. So if you have a Robbie the reindeer on the project, you’re gonna have a nightmare. Everybody’s gotta be… So that’s when I ask somebody on a duct cleaning project, so how long you been doing? Well, I’m a college student. I’m doing this for… And this is my first job. I think, my goodness.


RS: Sure.


TM: Do you think there’s a solution for sub-slab duct work that continuously gets wet?


NC: Nope. No.


TM: You’re shaking your head no?


NC: Solution is to fill it in with concrete, abandon the system and go elevated. We had that problem in our old childcare facility and I found that one of the first jobs I was in at DU, and I said, why are we doing this? ‘Cause my first mold inspection or second mold inspection I got involved with was a sub-slab duct work in a residential facility where the drain field was collapsed. So sewage water was coming back into the supply duct work that was underneath.


TM: Oh no.


NC: Yeah.


RS: Gross.


TM: Oh, what a disaster.


NC: It was humid and then also filled with lots of E. Coli.


RS: Yeah.


NC: So I said, well, why are you doing it in this childcare facility? And they said, well, it’s because it was… The architect said you bring the air up close to the kids, it’ll be more efficient. And so then I checked this place out and they covered up all the supplier duct work with mats. So we had no air changes.


TM: All the sub-slab duct work, all the supplies were covered up by carpets and objects?


NC: Yeah. Yes. And it’s because the people that are working there, they don’t know the system.


RS: Yeah.


TM: Yeah.


NC: You try to have a system that’s designed so that the people in the area don’t have to make very intelligent decisions about operation. They should just be able to walk in, everything runs itself, they’ve gotta focus on making sure the kids are happy and everything else. They don’t have to focus on, I need to do this change to make sure everything works right, ’cause if I don’t do this change, then all these people that are in this room with no ventilation get pneumonia and pass it among each other.


RS: Yeah. How about…


TM: Oh my gosh.


RS: Is there sub-slab duct work that just stays dry that is not problematic? What do you think?


NC: It’s really hard to keep them dry.


RS: Agreed. Yeah.


NC: And you also have equilibrium relative humidity problem. So that sub-slab duct work is typically colder than any other spot. And Cladosporium just says, you know, you built this environment just for me, even though it’s concrete and there isn’t any paper or anything, there’s just a modicum of dust on there. It’s just a little bit colder. So I’m gonna coat that whole duct work because it’s where I wanna be.


RS: Sure, sure. Okay.


NC: To be incredibly optimistic about it, they have a really good drain field, they’ve super insulated it. It might work, but a lot of things have to go right for it to work. And I don’t like something where everything has to go right.


RS: Yeah. Okay.


NC: Does that make sense?


TM: Well, what would you say…


RS: Yeah. Sounds like there’s no hope.




TM: It doesn’t have a lot going for it.


RS: We’re all doomed.




NC: Well, the first one we did at Williamson Hall was where they had sub-slab duct work in parts of it. And I’m wearing a tie and I’m crawling around the duct work. I didn’t wear a tie after that. But my tie is covered with mud in the supply duct work.


RS: My goodness.


TM: Oh. You were in the duct work, it was that large and you’re crawling around and it’s got mud in there?


NC: It has mud in the duct work. And that’s because the part that we haven’t talked about is geology. You really have to understand the geology, and a lot of places will build homes that look pretty nice, but they don’t understand that the underlying geology, that this used to be a bunch of potholes with clay lining everywhere. And so you pop the house right into this clay line and then they get any rain it comes in, fills the whole thing up.


TM: Oh sure, if it’s… Yeah.


NC: Ours was nice decor shale, which had this nice little spot that we dug out and then the water comes in and fills up the bathtub.


RS: Yuck.


NC: So you have to understand the geology in order for it to work. And if you get really well drained soil and everything’s fine, that’s gonna be okay.


TM: Neil, you know a lot about mold, you know a lot about building science. You know a lot about HVAC systems and construction and geology. [laughter] We could talk to you for hours and there’s so many topics that I still wanna dive into with you. But for sake of time, I think we should probably wrap up this podcast. What do you think, Reuben?


RS: Yeah. This has been amazing. A lot of stuff where it’s just like I don’t even know what I don’t know [chuckle], especially when you get into these commercial systems. This is fascinating to listen to.


TM: Yeah. One quick question I was gonna ask you, Neil, just wrapping up real fast. Do you have a recommendation for how homeowners, if they want to do some sort of like portable HEPA filtration system, is there a simple solution to that, a homemade option that people can use that you’d recommend?


NC: Well, I think it was mentioned by Mr. May, the Corsi-Rosenthal is a pretty good one. The other thing is that’s really neat is that there is overproduction of HEPA filters due to the pandemic. And a lot of places now are discounting them. So I’m getting some things that are 50% off. So I had something that was like $200 or 300$ and now it’s under $100. So you get the biggest filter you can and then the noise is the problem. So you ramp down the air flows just slightly. So you oversize it, run it at two or three, not on four. So you can still enjoy the HEPA filter part, but you don’t have the noise problem. Too many people buy it just for the size of the room, oversize it, turn it down. It’ll be wonderful.


RS: Excellent.


TM: Thank you so much, Neil. It’s been a pleasure having you on the show. Thank you for sharing all of your stories and your wisdom with us and hopefully we can get you back on again in the future.


NC: All right. Well, thank you very much for the questions.


RS: Yeah, thank you. For listeners, if you got any questions, thoughts, future show ideas, whatever, feel free to email us. We read all of our emails, it’s So I’m Reuben, for Tessa and Neil, saying thank you for listening. Take care.